It is necessary for a rider of a motor bicycle to wear a helmet when he drives the motor bicycle and, accordingly, it is also required to provide a space for safely keeping the helmet when he leaves the motor bicycle. In order to satisfy this requirement, there has been proposed a motor bicycle provided with a helmet accommodating box at a location above the engine unit and disposed in substantially the central portion of the motor bicycle body. For this arrangement, a fuel tank, which usually occupies this location, is displaced to another location such as, for example, a location disposed beneath the rider's.
According to this arrangement, however, the distance defined between the upper portion of the cover for the article accommodating box and the ground is increased for the reason that the article accommodating box has no degree of freedom in connection with the design thereof in comparison with that of the fuel tank and, hence, this particular location of the motor bicycle exhibits a relatively large height in the vertical direction. This increase in height also adversely affects the riding position of the rider. This problem is not so significant for a motor bicycle equipped with a V-type engine in which the height of the cylinder head can be designed to be relatively low or a motor bicycle equipped with a horizontally opposed two-cycle engine or a motor bicycle equipped with a vertical type two-cycle engine. However, the problem is significant for a vertical four-cycle engine utilizing cylinder heads each having a large volume. In addition, according to the described arrangement of the article accommodating box, the box is located above the cylinder head which is generally heated to a relatively high temperature and the article accommodating box is liable to be heated to a high temperature by means of the radiant heat from the cylinder head. The fact that the helmet accommodating box is highly heated adversely affects the helmet or other articles accommodated within the box. In order to obviate this problem, it may be possible to locate the article accommodating box at a position rearwardly of the cylinder head. This arrangement, however, affects the arrangement of the seat, and a reduction of the seating area of the seat due to the outer configuration and the large volume of the accommodating box is inconvenient for the rider.
In accordance with another aspect of the drawbacks or disadvantages of the prior art as described above, with respect to the arrangement of the article accommodating box, the fuel tank can be displaced to a location, for example, below the seat. However, in a conventional arrangement, a battery or the like is located at this position, so that it is difficult to accomodate a fuel tank with sufficient volume below the seat.
In accordance with a further aspect of the difficulties of the prior art, the article accommodating box is usually covered by means of a cover which is generally made of a metallic material, and which is thereford relatively easily heated to a high temperature by, for example, means of solar heat. The fact that the cover is heated to a high temperature adversely affects the helmet or the other articles accommodated within the accommodating box. In order to obviate this defect, it may be conceived to dispose a heat insulating material upon an inner surface of the cover. However, it is necessary for the heat insulating material to have a relatively large thickness for attaining a sufficient heat insulating effect. This fact results in increasing the volume or weight of the cover as well as increasing the manufacturing cost thereof. The volume of the accommodating box may also be correspondingly enlarged, which will finally affect the total layout or the design of the motor bicycle.
In accordance with the foregoing, therefore, the article accommodating box is generally provided with a ventilating hole for communication between the interior of the box and the atmosphere. The hole is generally open towards the advancing direction of the motor bicycle, so that during a rainy day rain drops may fall into the accommodating box through means of a horizontal passage of the ventilating hole during the travelling of the motor bicycle.
In accordance with a still further aspect of the prior art, it is required for the cover of the article accommodating box to be safely locked without failure and if the locking of the article accommodating box cover is not safely made, it is desired to inform the rider of this fact by any means.
In accordance with a still further aspect of the prior art, in a case where another person rides upon the motor bicycle, it is better for the motor bicycle to be equipped with an additional article accommodating box for accommodating a helmet for the other person when he leaves the motor bicycle.